CBQE-966: update smart_query test case

contains changes made query workload code.
using new 'idx' param to specify index key

Change-Id: Ieff65a18c0e59de397b24d2157a4c2a5089df68c
Reviewed-on: http://review.couchbase.org/25218
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>